Increased vascular permeability remains a critical determinant of morbidity and mortality in the ICU. There is overwhelming evidence that the endothelial glycocalyx plays an important role in determining the permeability of the microvascular wall. This surface layer is composed of entangled chains of proteoglycans, glycoproteins and adsorbed serum proteins that contribute to the formation of a `fiber-- matrix'. Experimental data regarding the structure-function relationship between surface glycoproteins and endothelial barrier properties is limited. The purpose of the proposed studies is to investigate the structure-function relationship of selected glycoproteins, which are major components of the endothelial glycocalyx, and their role in modulating endothelial barrier function. We hypothesize that cell-surface glycoproteins regulate endothelial barrier integrity by: 1) comprising the primary molecular sieve that determines microvascular permeability to water and serum proteins and, 2) through cytoskeletal interactions which modulate cell-cell adhesion, adherens junction organization, focal adhesion formation and, therefore, endothelial barrier function. Specific Aim #1 will define the contribution of specific glycoprotein components on endothelial barrier function. Specific Aim #2 will characterize the effect of altered expression of selected glycoproteins on endothelial barrier function. In Specific Aim #3 we will characterize the interaction of selected glycoproteins with the cytoskeletal and adherens junction proteins. Finally, In Specific Aim #4 we characterize the role of gycoproteins as shear stress sensors The PI, Dr. Randal Dull is committed to a career in academic medicine and research and to understanding the role of the glycocalyx in endothelial barrier regulation; this knowledge may lead to new therapeutic strategies to treat capillary leak syndrome. For example, novel resuscitation fluids composed of synthetic colloids could be developed that exploit cell-surface glycoprotein binding in order to normalize capillary permeability. This K08 will provide the foundation for a research career dedicated to understanding the molecular mechanisms of endothelial barrier regulation.